A flexible printed circuit having bump contacts or gold dot contacts is already known from U.S. Pat. Nos. 5,197,184 and 5,207,887 granted to William R. Crumly et al Mar. 30, 1993 and May 4, 1993 respectively.
An electrical connector employing such a flexible printed circuit is also known from U.S. Pat. No. 5,295,838 granted to James R. Whalen et al Mar. 22, 1994. In this electrical connector, the bump contacts or gold dot contacts of the flexible printed circuit are pressed against mating sets of contacts carried by a rigid circuit board by a clamping structure that is bolted to the rigid circuit board. The clamping structure includes an elongated pressure bar that engages the back side of the flexible printed circuit. The pressure bar has a plurality of blind holes aligned with the respective contacts of the flexible printed circuit. Each blind hole receives a compression spring that is compressed between the pressure bar and a pressure bar housing so that the pressure bar presses the electrical contacts of the flexible printed circuit against the mating set of electrical contact pads carried by the rigid circuit board.
“High-density” electrical connectors having raised bump or gold dot electrical contacts on one connector element adjacent a second connector element with electrical contact pads generally require a mechanism for providing compressive force urging the connector elements together to assure that electrical contact is maintained. Among the most successful prior approaches is an approach involving the provision of a spring-type element for maintaining pressure across the contact elements, particularly in combination with some external clamping arrangement as shown for example in U.S. Pat. No. 5,295,838. (Any electrical connector in which the pitch of the electrical contacts is between about 0.020 and about 0.050 mils is generally recognized as a high density electrical connector.)
Recently, the use of an elastomeric pad or layer having individual ridges aligned with each row of raised bumps has been adopted and widely accepted in the high-density connector field. By carefully aligning the ribs with the rows of bumps, reliable engagement force can be assured. A known 175 way “high density” electrical connector 1 of this type employing a flexible printed circuit 2 is illustrated in FIGS. 1 and 2. The flexible printed circuit 2 shown in FIG. 1 thus has 175 closely spaced contacts arranged rank and file with 7 rows of contacts each containing 25 contacts. In this high density electrical connector, an elongated elastomeric contact pressure pad 3 engages the flexible printed circuit to press the contacts 4 of the flexible printed circuit against the mating set of contact pads 5 carried by a rigid printed circuit board 6. The elastomeric pad 3 has twenty-five spaced ribs 7 that extend laterally across the elastomeric pad. Each rib 7 is aligned with a short transverse row of contacts and engages the back side of the flexible printed circuit pushing the contacts 4 against the contact pads 5 when the flexible printed circuit 2 and the elastomeric pad 3 are clamped between a clamp housing 8 and the printed circuit board 6. Clamp housing 8 is adjusted by machine screws 9 that screw into attachment portions of the clamp housing 8. Screws 9 pass through aligned locator holes in a stiffener bar 9a, printed circuit board 6 and flexible printed circuit 2 to align contacts 4 with contact pads 5 and the ribs 7 with the short rows of contacts 4.